Many variants of vehicle dynamics control systems in which the actual motion of the vehicle is compared with a desired motion are known. A desired vehicle motion is usually calculated by means of a vehicle model on the basis of variables which represent or affect the state of the vehicle. This calculated variable is compared with the corresponding measured variable. Depending on the deviation between the variables, actuators are then driven, which affect the vehicle dynamics. For example, it is known that a one-track model can be used to calculate a desired angular yaw rate (rotational velocity around the normal axis of the vehicle) as a function of the measured vehicle longitudinal velocity and the measured steering wheel angle and to compare this calculated rate with the angular yaw rate actually being measured. As a function of this comparison, it is then possible to influence the wheel brakes, the drive torque, the wheel suspensions, and/or the steering systems of the vehicle to achieve the desired vehicle dynamics. Instead of the desired yaw rate, however, it is also possible, as a substitute, to compare the desired difference between the rotational speeds of the front wheels with the corresponding actual value.
It is important in vehicle models of this type to have the most accurate possible knowledge of the influences which are exerted by the vehicle's tires. Such influences are usually expressed by the "skew stiffness". When the tires of the vehicle are replaced and thus when the actual skew stiffnesses differ from the values used in the one-track model mentioned above, then the vehicle motion which is calculated as the specified (desired) value differs from the motion actually desired. As a result, the wrong measures are taken to drive the actuators (brakes, engine, steering, and/or wheel suspension). An example of how the skew stiffness is used to calculate a desired vehicle motion is disclosed in U.S. Pat. No. 5,371,677, which is incorporated herein by reference.